package org.apache.lucene.index;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

/**
 * This is a {@link LogMergePolicy} that measures size of a segment as the total
 * byte size of the segment's files.
 */
public class LogByteSizeMergePolicy extends LogMergePolicy {

	/**
	 * Default minimum segment size.
	 * 
	 * @see setMinMergeMB
	 */
	public static final double DEFAULT_MIN_MERGE_MB = 1.6;

	/**
	 * Default maximum segment size. A segment of this size or larger will never
	 * be merged.
	 * 
	 * @see setMaxMergeMB
	 */
	public static final double DEFAULT_MAX_MERGE_MB = (double) Long.MAX_VALUE;

	public LogByteSizeMergePolicy() {
		super();
		minMergeSize = (long) (DEFAULT_MIN_MERGE_MB * 1024 * 1024);
		maxMergeSize = (long) (DEFAULT_MAX_MERGE_MB * 1024 * 1024);
	}

	protected long size(SegmentInfo info) throws IOException {
		return info.sizeInBytes();
	}

	/**
	 * <p>
	 * Determines the largest segment (measured by total byte size of the
	 * segment's files, in MB) that may be merged with other segments. Small
	 * values (e.g., less than 50 MB) are best for interactive indexing, as this
	 * limits the length of pauses while indexing to a few seconds. Larger
	 * values are best for batched indexing and speedier searches.
	 * </p>
	 * 
	 * <p>
	 * Note that {@link #setMaxMergeDocs} is also used to check whether a
	 * segment is too large for merging (it's either or).
	 * </p>
	 */
	public void setMaxMergeMB(double mb) {
		maxMergeSize = (long) (mb * 1024 * 1024);
	}

	/**
	 * Returns the largest segment (meaured by total byte size of the segment's
	 * files, in MB) that may be merged with other segments.
	 * 
	 * @see #setMaxMergeMB
	 */
	public double getMaxMergeMB() {
		return ((double) maxMergeSize) / 1024 / 1024;
	}

	/**
	 * Sets the minimum size for the lowest level segments. Any segments below
	 * this size are considered to be on the same level (even if they vary
	 * drastically in size) and will be merged whenever there are mergeFactor of
	 * them. This effectively truncates the "long tail" of small segments that
	 * would otherwise be created into a single level. If you set this too
	 * large, it could greatly increase the merging cost during indexing (if you
	 * flush many small segments).
	 */
	public void setMinMergeMB(double mb) {
		minMergeSize = (long) (mb * 1024 * 1024);
	}

	/***************************************************************************
	 * Get the minimum size for a segment to remain un-merged.
	 * 
	 * @see #setMinMergeMB
	 **************************************************************************/
	public double getMinMergeMB() {
		return ((double) minMergeSize) / 1024 / 1024;
	}
}
